Syntheses and electrochemical properties of the Na-doped LiNi0.5Mn1.5O4 cathode materials for lithium-ion batteries

Abstract

The novel Na-substituted Li1-xNaxNi0.5Mn1.5O4 has been synthesized to use as a cathode material for lithium ion battery via a solid-state method. Both crystal domain size and lattice parameter are influenced by the doping content of Na, without changing the basic spinel structure. The doping of Na ions not only increase the disordered distribution of nickel and manganese cations in spinel, but also increase two additional electron hopping paths, which contribute to a better charge transfer ability, relieve the ohmic polarization and electrochemical polarization of materials and improve lithium ion diffusion coefficient. After Na-doped, the discharge specific capacity rises up comparing to the sample without Na-doped. As a result, the excellent rate capability is achieved for the doping content of 5% Na in spinel, that the discharge capacity is increased by 3.4%, 9.4%, 9.1%, 8.7%, 6.5% and 3.4% in comparison with LNMO, presenting a discharge specific capacity of 121, 119.4, 118.5, 115.1, 108.4 and 101.3mAh·g−1 at the rates of 0.2, 0.5, 1, 2, 5 and 10C respectively, with tiny Mn3+ platform appearing. In addition, the sample presents a discharge capacity of 125mAh·g−1 at 1C, with a retention of 116.2mAh g−1 after 100 cycles. Even cycling at 5C rate and 55°C, the cell with 5% Na-doped LNMO cathode can has 82% of capacity retention after 400 cycles, indicating that it is a promising cathode material for lithium ion batteries.